Abnormal pigmentation of the skin is commonly seen in dermatologic practice. A subject's skin may have pigmentation abnormalities due to vascular lesions, pigmented lesions, or tattoos. Vascular lesions, such as port wine stain birthmarks, telangiectasia and hemangiomas, are characterized by abnormally enlarged blood vessels. Pigmented lesions are non-vascular disfigurements of the skin caused by an abnormally high concentration of melanin in localized areas of the skin. Such pigmented lesions include freckles, age or liver spots, cafe au lait birthmarks, lentigines, nevi, melanomes, nevus of Ota and lentigo maligna. Tattoos may be divided into two categories, including self-inflicted tattoos and traumatic tattoos. Traumatic tattoos are created during an accident which causes a scrape or abrasion such that a foreign material becomes imbedded in the skin.
Pulsed laser systems, such as those manufactured by Candela Laser Corporation, have been widely used by plastic surgeons and dermatologists to successfully treat pigmentation abnormalities on the face and other areas of the human body for obvious cosmetic reasons. For example, Candela's Pigmented Lesion Laser has been used to lighten or remove pigmented lesions. Candela's TATULAZR has been used to remove blue/black tattoos. Candela's Vascular Lesion Laser has been used to lighten or remove vascular lesions.
These and other such laser systems typically include a pulsed laser and a delivery system. The delivery system includes a handpiece that delivers pulses of laser radiation to a subject'skin typically having a circular cross-section ranging from 1-10 mm in spot diameter. The treatment procedure generally involves irradiating an area of a subject's skin including a pigmentation abnormality with a beam of pulsed laser radiation.
Undesirable side effects of laser treatment include purpura, hypopigmentation and hyperpigmentation. Purpura is generally attributed to the damage to the skin's microvasculature which results in the treated area of the subject's skin turning blue/black in appearance. Purpura can take up to two weeks to clear and is particularly bothersome when the treated area is on a subject's face. Hyperpigmentation can be caused by the deposition of hemosiderin, a blood breakdown by-product in the skin, which occurs due to damage to the blood vessels. This can result in the treated area of the subject's skin turning brown some days after the treatment and is particularly common when the vessels treated are on the legs. Hyperpigmentation is slow to clear, sometimes taking up to a year to go away. Hypopigmentation is attributable to damage to the melanin-producing cell in the skin. Hypopigmentation is generally transient, but is cosmetically undesirable while it persists.
In treating a pigmentation abnormality which is distinct and clearly demarcated, it is advantageous to irradiate the area of the skin including the abnormality while minimizing exposure of the adjacent normally pigmented tissue to radiation. This results in reduced purpura, hypopigmentation and hyperpigmentation. One technique used involves manipulating the handpiece to trace out or scan the area of the skin including the pigmentation abnormality with the laser pulses having a circular cross-sectional area or spot. In cases where the pigmentation abnormality is elongated in shape, to minimize the exposure of adjacent normally pigmented skin, a pulsed beam with a smaller cross-sectional area is used on the area of the skin including the abnormality. It has been found clinically that using pulses with a small cross-sectional area (spot diameter of 3 mm or less) results in much less purpura and reduced incidence of hypopigmentation and hyperpigmentation.
One problem with this technique, however, is that treatment is quite tedious, since only a small portion of the targeted pigmentation abnormality is irradiated for each laser pulse. Thus, the number of pulses required to treat a pigmentation abnormality and the treatment time increase significantly.